The present invention relates to coating surfaces of blow-molded plastic containers, and more particularly, the present invention relates to a process for continuously blow-molding and coating plastic containers which are retained under positive control throughout the molding and coating processing steps.
It is known to provide a coating on blow-molded plastic containers and to cure the applied coating. The coatings can include colorants, ultra-violet light protectors, barrier materials and the like, and can be applied on the inside or outside surfaces of the containers. For examples of patents disclosing methods of applying coatings to containers, see U.S. Pat. No. 4,515,836 issued to Cobbs, Jr. et al.; U.S. Pat. No. 4,569,869 issued to Kushida et al.; U.S. Pat. No. 4,809,640 and U.S. Pat. No. 4,818,571 issued to Pilley et al.; U.S. Pat. No. 4,730,575 issued Jenkins; U.S. Pat. No. 3,902,453 issued to Frische; U.S. Pat. No. 5,308,649 issued to Babacz; U.S. Pat. No. 4,391,381 issued to Ota et al.; U.S. Pat. No. 3,804,663 issued to Clark; U.S. Pat. No. 3,833,406 issued to White; U.S. Pat. No. 4,331,250 issued to Rawe et al.; and U.S. Pat. Nos. 4,254,170 and 4,267,143 issued to Roullet.
One known process for manufacturing containers includes injection molding preforms of plastic, such as PET, and blow-molding the preforms in a mold cavity. The finish of the preform can be retained under positive control while the preform is processed through blow molding machinery. The positive control can be accomplished by equipment which grasps the neck of each preform such as disclosed in U.S. Pat. No. 5,683,729 issued to Valles.
After molding, the resulting containers are discharged from the mold and released from positive control by, for instance, being placed on a transfer conveyor which leads to further operations such as packing and shipping operations. It is also known to transfer the containers via transfer conveyors to other stations which accomplish further operations such as filling and capping.
As discussed previously, further operations can also include applying a coating to the exterior surface of the container and curing, or drying, the coating on the container. Conventional coating/curing operations are carried out in machinery separate and apart from blowing, filling and capping equipment. Thus, conventional coating equipment requires additional floor space, transfer conveyors and container handling apparatus, and creates an increased potential for container contamination.
U.S. Pat. No. 3,547,294 issued to Williams discloses a continuous process of extrusion blow molding a container, promptly applying a coating on a surface of the container, and then, filling and capping the container. The coating disclosed in Williams is for sealing in the flavor of the liquid stored in the container or for protecting the liquid from ultra-violet light. The Williams patent also discloses applying the coating in a refrigerated atmosphere, or alternatively, in a heating chamber.
Although various ones of the above-referenced methods for coating containers may be satisfactory for their intended purposes, there is a need for an improved coating method which reduces the required floor space for machinery, increases the handling efficiency of preforms and containers, eliminates contamination of the preforms and containers, and reduces the number of required transfer conveyors. In addition, the method according to the present invention applies the coating to the containers when the containers are at elevated temperatures due to being freshly blown, or freshly hot-filled, so that curing of the coating is initiated and bonding of the coating to the container surface is improved.
With the foregoing in mind, an object of the present invention is to provide a novel process for efficiently blow-molding and coating plastic containers.
Another object of the present invention is to provide an improved process for handling preforms and resultant blown containers from the time they enter blow molding machinery until after they have been coated.
A further object of the present invention is to provide a unique process for efficiently curing a coating applied to either an empty, or a hot-filled, container.
As another object, the present invention provides an improved coating process for maintaining sterility of the containers during blowing, coating, curing, filling and capping operations.
More specifically, in the process of the present invention, a plurality of preforms are advanced in sequence under positive control into a blow-mold where they are blow-molded into containers. The blown containers are discharged from the blow-mold under positive control and at an elevated temperature. Thereafter, the containers are coated while remaining under positive control and while being at an elevated temperature. Thus, the preforms and resulting containers are maintained under continuous positive control throughout the entire container blow-molding and coating process, and curing and bonding of the coating is initiated and enhanced by the elevated temperature of the containers at the time of coating. Also, curing temperatures can be elevated, for instance, from 150xc2x0 F. to 190xc2x0 F., due to heat set blow molding processes and to the low moisture content of the container at the time of curing. The elevated curing temperatures reduce the required curing time and increase the speed of the overall process.
Preferably, the coating is promptly applied to empty containers after being discharged from hot blow molds to take advantage of the residual heat of the containers to initiate drying and curing of the coating. Alternatively, the blow molded bottles are first hot-filled and capped before being promptly coated to take advantage of the residual heat of the hot-filled containers to initiate drying and curing of the coating.